Cod sursa(job #1339763)
Utilizator | Data | 11 februarie 2015 09:33:22 | |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 100 |
Compilator | cpp | Status | done |
Runda | Arhiva educationala | Marime | 0.64 kb |
#include <iostream>
#include <fstream>
#include <cstdio>
using namespace std;
ofstream g("ciur.out");
unsigned char a[1000005];
int j,i,n,k;
int main()
{
freopen("ciur.in","r",stdin);
scanf("%d",&n);
for(i=1;i*i<=n/2;i++)
{
if(a[i]==0)
{
for(j=3*i+1;j<=n/2;j=j+2*i+1)
a[j]=2;
}
}
i=1;
for(k=1;k<=n/2;k++)
{
if(a[k]==0)
{
if(2*k+1<=n)
{
//g<<2*k+1<<" ";
//if(k<n/2)
// g<<",";
i++;
}
}
}
g<<i<<'\n';
return 0;
}